How Does Air Move Around the Globe?
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Transcript of How Does Air Move Around the Globe?
How Does Air Move Around the Globe?
Review of last lectureReview of last lecture
• Thickness of the atmosphere: less than 2% of Earth’s thickness
• Definition of temperature. 3 units. • Four layers of the atmosphere, what separate them?• Definition of pressure and its unit. • Definition of pressure gradient. Pressure gradient sets
the air in motion.• Equation of state (Relationship between P, ρ, and T)• Vertical Pressure Distribution. How does pressure
change with height? What is the hydrostatic equilibrium?
Review of last lecture (cont.)Review of last lecture (cont.)
• Know 3 Forces that affect wind speed /direction• Especially work on Coriolis force, as this is the
hardest to understand. Which direction is air deflected to by Coriolis force?
• What is the geostrophic balance? At which level is it valid? Difference between upper level and surface winds
• Does cyclones correspond to high or low surface pressure? Is the air moving clockwise or counter-clockwise around them? How about anticyclones?
• What are the troughs and ridges?
The most common atmospheric The most common atmospheric circulation structurecirculation structure
L
H
H
L
HeatingCoolingor No Heating
Imbalance of heating Imbalance of temperature Imbalance of pressure Wind
IntroductionIntroduction• Well-defined heating, temperature and pressure patterns exist
across the globe• These define the general circulation of the planet• In describing wind motions:
– Zonal winds (east-west): flow parallel to lines of latitude• Flowing eastward: Westerly wind• Flowing westward: Easterly wind
– Meridional winds (north-south): flow parallel to lines of longitude
• Flowing northward: Southerly wind• Flowing southward: Northerly wind
Annual mean precipitation (heating)Annual mean precipitation (heating)
Extratropical stormtrack
Tropical rainfall
Extratropical stormtrack
Primary Highs and LowsPrimary Highs and Lows
Equatorial low
Subtropical high
Subpolar low
Polar high
Zonal mean circulation
Each hemisphere is divided into 3 distinct cells:
Hadley Cell
Ferrel Cell
Polar Cell
Three-cell modelThree-cell model
Vertical structure and mechanismsVertical structure and mechanisms
Hadley Cell (thermal): Heating in tropics forms surface low and upper level high air converges equatorward at surface, rises, and diverges poleward aloft descends in the subtropics
Ferrel Cell (dynamical): Dynamical response to Hadley and polar cells
Polar Cell (thermal): Driven by heating at 50 degree latitude and cooling at the poles
HadleyPolar
Zonal mean structure of temperatureZonal mean structure of temperature
Two characteristics:
• Horizontally uniform in the tropics
• Steep gradient in the extratropics
Vertical structure of zonal windVertical structure of zonal wind
Two characteristics:
• Westerly winds in the extratropical troposphere (caused by the Coriolis force). Explains why storms move eastward, flight times
• Jet streams: local maximum of winds (caused by sharp pressure gradient across the boundary between warm tropical air and cold polar air)
• Caused by steep temperature gradients between cold and warm air masses
• Polar front - marks area of contact, steep pressure gradient polar jet stream
• Low latitudes subtropical jet stream
• Stronger in winter, affect daily weather patterns
The Jet StreamsThe Jet Streams
Low pressure centers: weather and precipitation
High pressure centers: warm, drought and desert
South Pacific high
South Atlantic high
South Indian high
Semipermanent Pressure Cells: NH winter
South Pacific high
South Atlantic high
South Indian high
Semipermanent Pressure Cells: NH summer
• Ocean surface currents – horizontal water motions• Transfer energy and influence overlying atmosphere• Surface currents result from frictional drag caused by
wind - Ekman Spiral
General circulation of the oceansGeneral circulation of the oceans
• Water moves at a 45o angle (right) in N.H. to prevailing wind direction
• Due to influence of Coriolis effect
• Greater angle at depth
• Surface currents mainly driven by surface winds• North/ South Equatorial Currents pile water westward, create the Equatorial Countercurrent• western ocean basins –warm poleward moving currents (example: Gulf Stream)• eastern basins –cold currents, directed equatorward
Global surface currentsGlobal surface currents
SummarySummary• Three precipitation (heating) belts. Primary high and
lows• Three-cell model. Mechanism for each cell• Two characteristics of zonal mean temperature structure• Two characteristics of zonal mean wind structure. Why
does westerly winds prevail in the extratropical troposphere? What cause the jet streams?
• Semipermanent pressure cells. Low pressure is associated with clouds and precipitation. High pressure is associated with warm surface temperature, drought, and desert.
• What drives the ocean surface currents? In the case of Ekman spiral, what is the direction of surface current relative to surface wind?
Works citedWorks citedImages•http://pulleysandgears.weebly.com/gears.html •http://visual.merriam-webster.com/earth/meteorology/meteorological-measuring-instruments/measure-wind-direction.php